Machine felt comprising woven fabric having fibrous batt needled thereto

ABSTRACT

Machine felts comprising a base fabric having a batt needled to one or both sides, the machine felt being suitable for use in the paper, cellulose and asbestos-cement industries, the base fabric having longitudinal spun yarns made of wool and/or synthetic staple fibres or multifilaments and transverse yarns made entirely or partially of plastic monofilaments having preferably a thickness of 0.2-0.6 mm.

United States Patent 11 1 1111 3,839,136 Eriksson 1 Oct. 1, 1974 [54] MACHINE FELT COMPRISING WOVEN 2,959,509 11/1960 Marshall 161/81 FABRIC HAVING FIBROUS BATT 3,207,659 9/1965 Wagner 161/92 NEEDLED THERETO 3,230,599 l/l966 McKew et al 28/722 [75] Inventor: Erik Birger Eriksson, Halmstad, FOREIGN PATENTS QR APPLICATIONS Sweden 686,777 5/1964 Canada 139/420 [73] A i N di Maskinfilt Aktiebolaget, 982,801 2/1965 Great Britain 28/722 Halmstad, Sweden [22] Filed; Oct, 3, 1969 Primary Examiner-George F. Lesmes 1 pp NO 863 653 Assistant Examiner.lames J. Bell [30] Foreign Application Priority Data [57] ABSTRACT OCI. 7, 1968 Sweden 13489/68 Machme felts compnsmg a base fabric havmg a batt 152 US. Cl 161/80, 28/722, 161/85, needled to one or both Sides, the Imwhine felt bemg 161/89, 161/91, 161/92, 161/95, 161/154 suitable for use in the paper, cellulose and asbestos- 51 Int. Cl B32b 5/06 Cement industries, the base fabric having longltudmal [58] Field 61 Search 161/80, 85, 91, 92, 154, Spun yams made of wool and/0r Syntheflc Staple fibres 9 161/169, 170, 81, 89, 95; 2 72 0r multifilaments and transverse yarns made entirely 3 5 or partially of plastic monofilaments having preferably a thickness of 0.2-0.6 mm.

[56] References Cited UNITED STATES PATENTS 3 Claims, 3 Drawing Figures 2,903,021 9/1959 Holden ct al. 139/425 S //I 2 4 j .1 y \l j 7 f V Z;

PATENTEBUBT H974 IN VEN TOR 'F/K 5/2652 ate/(550M BY 6 WM ,mw w

A fTORA/E Vs MACHINE FELT COMPRISING WOVEN FABRIC HAVING FIBROUS BATT NEEDLED THERETO BACKGROUND OF THE INVENTION This invention relates to paper machine felts comprising a base fabric having batts needled to one or both sides. The machine felt may be used in the paper, cellulose and asbestos-cement industries.

Needled felts for the paper, cellulose and asbestoscement industries are presently manufactured by necdling one or more fibrous batts to a woven base fabric. The base fabric consists of spun threads made of wool 'and/or synthetic staple fibres or multifilaments. When needling the batt and during subsequent completion of the machine felt, involving inter alia washing, various chemical treatments, and drying under tension) the width of the machine felt is reduced by shrinkage, and such width shrinkage may amount to 35 percent. One consequence of this width shrinkage is that the base fabric and therewith the entire machine felt becomes denser and more compact. on the one hand because the longitudinal yarns of the base fabric are more closely spaced, and on the other hand because the fibres in the batt are drawn nearer to each other and also nearer to the thread system of the base fabric. The initial width, during manufacture of needled felts, is therefore kept considerably larger than the final desired width of the machine felt, and this involves considerable investment due to the necessity to obtain wider machinery. A further disadvantage is a variation in width shrinkage which can occur in the otherwise identical machine felts and which requires that the machine felts have to be manufactured with a large safety margin in respect oftheir width. The variation in the width of the felt may result in variation in the basis weight and permeability of the felt.

The service life of a machine felt in the pressing zone of a paper machine is normally limited by the gradual decrease in its permeability due to clogging. This reduction in permeability gives so called crushing of the paper web during its passage through the press nip and results in a replacement of the machine felt.

Thus, it is extremely desirable to be able to manufacture machine felts which are open as possible, i.e., having the largest possible permeability for air or water. Various manufacturing techniques may be adopted, such as for example the use of an open base fabric and the use of fibre mixture, inter alia, manufactured from coarse fibres. However, the manufacture of a base fabric in which the longitudinally directed yarns from the beginning are greatly spaced apart, is not an effective solution, since this results during processing in a correspondingly higher degree of width shrinkage than is obtained with a normal base fabric and consequently does not produce any substantial change in the permeability of the felt. The use of coarse fibres in the batt may to some extent produce a more open felt, but the danger of marking greatly restricts such procedure. Furthermore, coarse fibres in the batt by no means prevent widthwise shrinkage.

Base fabric yarns made from wool and/or synthetic staple fibres or multifilaments may treated with a resin, thus achieving a stiffening or reinforcing effect. However. this process does not yield expected advantages, since the stiffness or rigidity substantially disappears during needling and subsequent processing.

Thus, the width shrinkage largely remains considerable, with a a corresponding reduction in permeability.

SUMMARY OF THE INVENTION The present invention aims to reduce to a minimum the above-discussed defects by providing machine felts having a base fabric with transverse yarns entirely or partially of plastic monofilaments having a thickness of preferably 0.2 0.6 mm.

Accordingly, this invention provides a machine felt comprising a base fabric having a batt needled to one or both of its sides, the base fabric having longitudinal yarns spun of wool and/or synthetic staple fibres or multifilaments and transverse yarns made entirely or partially of plastic monofilaments. Because the monofilaments are not compressed in the longitudinal direction and the needled-on batt prevents the monofilamerits from forming curved elements or eyelets, machine felts can be manufactured without substantial width shrinkage. For purposes of comparison, the total width shrinkage calculated from the differance between the original width of the base fabric and the final felt width, is, when using normal base fabrics, approximately 35 percent and, when using base fabrics according to the present invention only approximately 10 percent. The variation in this latter width shrinkage is insignificant when compared with hitherto width shrinkage variations in machine felts having normal base fabrics. It may thus be considered that the machine felts of this invention are almost uniform and assist with respect to width shrinkage in considerably reducing the safety margin. This relatively uniform width shrinkage furthermore assists in considerably reducing the variation of the final basis weight and of the permeability of otherwise identical machine felts.

The effect when using monofilaments only in the transverse direction of the base fabric is so considerable that it is possible to sufficewith only a relatively small proportion of such monofilaments, and still retain a high degree of widthwise stability. It is therefore possible to manufacture needled press felts having a basis weight of for example 1000 g/m and containing a base weave of only 250 g/m' The transversely directed monofilaments only need to constitute, for example, 30 percent (approximately 80 g/m') of the total basis weight of the base fabric. A base fabric of this kind is, per se, extremely permeable and, due to the selection of relatively fine monofilaments, marking on the paper web is very slight. The use of fine, smooth and compact monofilaments in the transverse direction of the base fabric causes a lower resistance to water flow in the longitudinal direction of the machine felt, as compared with normal base fabrics.

In connection with dewatering in presses where large.

quantities of water are required to be removed, for example in a first press of a kraft liner machine, it is considered to be an advantage that machine felts contain coarse and shape-retaining yarns which in the machine felt form mesh or loops into which the water is able to penetrate and be conveyed away. During manufacture of such machine felts it is necessary, in order to be able to retain a desired coarse yarn structure of the base fabric, to build up the latter in such manner that it contains both spun yarns and monofilaments in the transverse direction. There are various different processes which make it possible to use the monofilaments parallel with ordinary spun yarns or multifilaments, to twist the monofilaments with spun yarns or multifilaments or to replace certain conventional yarns with monofilaments. Whichever mode of procedure may be selected, a reduction in the width shrinkage, with correspondingly retained good openness, as discussed hereinabove, is always achieved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a portion ofa machine felt according to the invention during manufacture,

FIG. 2 is a cross-section through the said machine felt at a later stage of its manufacture, and

FIG. 3 is a perspective view of a portion of one type of a base fabric.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT The machine felt shown in FIG. 1 consists of a base fabric 1 having longitudinal yarns 2 (with respect to machine direction of the machine felt) and transverse yarns 3. The yarns 2 are made from spun filaments of wool and/or staple fibres or multifilaments, and the yarns 3 consist entirely or partially of monofilaments. The base fabric 1 has been shown exposed on the lefthand side of FIG. 1 to clearly show the relative positions of yarns 2 and 3. In a central portion of the machine felt, the batt 4 on one side has been partially needled down onto the base fabric and, at the right-hand portion, the batt has been completely needled to the base fabric.

Referring to FIG. 2, a batt 5 is attached to the opposite side of the base fabric. The fibres of this batt 5 are caused, in the same manner, to penetrate partially into and through the base fabric 1 and the already attached batt 4.

Many types of yarns 3 may be employed in the ma chine felt, their selection, with reference to the density of the base fabric 1, being mainly based on manufacturing and technical factors and the desired properties of the machine felt. Thus, for example the yarns 3 may be polyamide monofilaments having 8-10 filaments per cm. and a yarn diameter of for example 0.3 mm. The monofilaments may vary in thickness from 0.2 mm to 0.6 mm.

Referring to FIG. 3, the base fabric is composed of longitudinal yarns 2 and transverse yarns 3. The yarns 3 consist of cores of monofilaments 3 around which are wound yarns 3". These yarns 3" may be spun of wool and/or synthetic staple fibres or multifilaments.

What I claim is:

l. A shape-retaining machine felt, which undergoes reduced width-shrinkage during its manufacture, for use in dewatering presses and other operations in which water penetrates the felt and is carried away, comprismg:

a base woven fabric of longitudinal yarns spun from short staple fibers selected from the group consisting of wool fibers, synthetic staple length fibers and blends of said wool and snythetic staple length fibers, and of transverse yarns comprising fine synthetic thermoplastic monofilaments having a thickness of 0.2 0.6 millimeters; and,

a fibrous batt needled to at least one surface of said base fabric with the fibers of the batt penetrating into the base fabric.

2. A machine felt according to claim I, wherein the monofilaments have spun yarns twisted around them.

3. A machine felt according to claim 2, wherein the spun yarns are so twisted around the monofilaments that the monofilaments constitute a core in the transverse yarns. 

1. A SHAPE-RETAINING MACHINE FELT, WHICH UNDERGOES REDUCED WIDTH-SHARINKAGE DURING ITS MANUFACTURE, FOR USE IN DEWATERING PRESSES AND OTHER OPERATIONS IN WHICH WATER PENETRATES THE FELT AND IS CARRIED AWAY, COMPRISING: A BASE WOVEN FABRIC OF LONGITUDINAL YARNS SPUN FROM SHORT STAPLE FIBERS SELECTED FROM THE GROUP CONSISTING OF WOOL FIBERS, SYNTHETIC STAPLE LENGTH FIBERS AND BLENDS OF SAID WOOL AND SNYTHETIC STAPLE LENGTH FIBERS, AND OF TRANSVERSE YARNS COMPRISING FINE SYNTHETIC THERMOPLASTIC MONOFILAMENTS HAVING A THICKNESS OF 0.2-0.6 MILLIMETERS, AND, A FIBROUS BATT NEEDLED TO AT LEAST ONE SURFACE OF SAID BASE FABRIC WITH THE FIBERS OF THE BATT PENETRATING INTO THE BASE FABRIC.
 2. A machine felt according to claim 1, wherein the monofilaments have spun yarns twisted around them.
 3. A machine felt according to claim 2, wherein the spun yarns are so twisted around the monofilaments that the monofilaments constitute a core in the transverse yarns. 